Myxedema megacolon

The thyroid and the gut

Thyroid disease is common, and its effects on the gastrointestinal system are protean, affecting most hollow organs. Hashimoto disease, the most common cause of hypothyroidism, may be associated with an esophageal motility disorder presenting as dysphagia or heartburn. Dyspepsia, nausea, or vomiting may be due to delayed gastric emptying. Abdominal discomfort, flatulence, and bloating occur in those with bacterial overgrowth and improve with antibiotics. Reduced acid production may be due to autoimmune gastritis or low gastrin levels. Constipation may result from diminished motility, leading to an ileus, megacolon, or rarely pseudoobstruction. Ascites in myxedema is characterized by a high protein concentration. Graves' disease accounts for 60% to 80% of thyrotoxicosis. Hyperthyroidism is accompanied by normal gastric emptying with low acid production, partly due to an autoimmune gastritis with hypergastrinemia. Transit time from mouth to cecum is accelerated, resulting in diarrhea. Steatorrhea is due to hyperphagia and stimulation of the adrenergic system. Diarrhea in medullary carcinoma of the thyroid (MCT) may be due to elevated calcitonin, prostaglandins, or 5-hydroxyindoleacetic acid. Ileal or colonic function may be abnormal. The esophagus may be compressed by benign processes, but more often by malignancies. MRI and CT scans are the best diagnostic modalities. The gastrointestinal manifestations of thyroid disease are generally due to reduced motility in hypothyroidism, increased motility in hyperthyroidism, autoimmune gastritis, or esophageal compression by a thyroid process. Symptoms usually resolve with treatment of the thyroid disease.

An unusual case of myxedema megacolon with features of ischemic and pseudomembranous colitis

Myxedema megacolon is rare; usually, it manifests with abdominal distention, flatulence, and constipation. Herein we describe a 72-year-old man who had intermittent diarrhea, bloating, and abdominal pain for more than a year. Cultures of stool specimens for Clostridium difficile enterotoxin were variably positive and negative. Colonoscopic biopsy specimens were thought to be consistent with chronic ischemia. Thyroid function tests showed severe hypothyroidism; the patient's symptoms resolved with thyroid hormone replacement. We hypothesize that gross dilatation of the colon, attributed to myxedema, was followed by intestinal ischemia and complicated by recurrent episodes of pseudomembranous colitis. A review of the relevant literature is provided. This unusual manifestation of myxedema should be considered in the differential diagnosis when a patient has diarrhea, bloating, and abdominal pain.

Radiology in intestinal ischemia. Plain film, contrast, and other imaging studies

Because plain films are usually normal or nonspecific in both colonic and acute mesenteric ischemia, they are not diagnostically helpful. The barium enema is the most useful radiographic examination in the diagnosis of colonic ischemia, and a double-contrast study will show abnormalities in almost all cases. Findings specific for colonic ischemia characteristically change with time. Thumbprinting is the most diagnostic finding; it is seen early in the course of the disease and usually resolves or is replaced within 1 or 2 weeks by an acute ulcerating colitis pattern. The latter may heal over months or go on to stricture formation or a persistent colitis. Nonspecific abnormalities can also be identified on CT and ultrasound, but the incidence of the findings with colonic ischemia is not known. Plain film findings occur late in the course of acute mesenteric ischemia and thus cannot be relied on for the diagnosis, although they may be useful in excluding other conditions. When acute mesenteric ischemia is suspected, angiography should be performed, but CT, ultrasound, and, perhaps, MR imaging may contribute to the diagnosis.

Myxedema megacolon after external neck irradiation

Myxedema megacolon is a rare manifestation of hypothyroidism. It may respond to appropriate treatment but is sometimes irreversible, resulting in fatal complications. Two possible mechanisms to explain the colonic atony include (1) myxomatous infiltration of the submucosa with separation of the muscular fibers from the ganglia of Auerbach's plexus, and (2) severe autonomic neuropathy affecting the extrinsic nerves to the colon and the myenteric plexus. Histology from our case supports the first proposed mechanism. Urecholine challenge and manometric measure response may help predict reversibility of colonic atony. Treatment should be individualized and should include factors such as age, duration of symptoms, and other medical illness. Low-dose oral or intravenous triiodothyronine is effective. Hypothyroidism following external radiation of the neck for lymphoma is not uncommon, and the risk increases following one or more lymphangiograms. Such patients should be followed up with regular TSH estimations for at least three years.